Relevant parts of this background description are also a part of embodiments of the disclosed invention.
Several floor panels on the market are installed in a floating manner with mechanical locking systems formed at the long and short edges. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the panel. Alternatively, parts of the locking system may be formed of a separate material, for instance aluminum or plastic material, which is integrated with the floor panel, i.e. joined with the floor panel in connection with the manufacture thereof.
Laminate flooring usually comprise a 6-8 mm wood based core, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1 mm thick lower balancing layer. The laminate surface and the balancing layer comprise melamine-impregnated paper. The most common core material is fibreboard with high density and good stability usually called HDF—High Density Fibreboard. The impregnated surface and balancing papers are laminated to the core with heat and pressure. HDF material is hard and has a low flexibility, especially in the vertical direction perpendicular to the fibre orientation.
Recently a new type of powder based laminate floors has been introduced. Impregnated paper is replaced with a dry powder mix comprising wood fibres, melamine particles, aluminum oxide and pigments. The powder is applied on an HDF core and cured under heat and pressure. Generally high quality HDF is used with a high resin content and low water swelling. Advanced decors may be formed with digital printing. Water based ink is injected into the powder prior to pressing.
Luxury vinyl tile, LVT, flooring with a thickness of 3-6 mm usually comprises a transparent wear layer which may be coated with an ultraviolet, UV, cured polyurethane, PU, lacquer and a decorative plastic foil under the transparent foil. The wear layer and the decorative foil are laminated to one or several core layers comprising a mix of thermoplastic material and mineral fillers. The plastic core may be rather soft and flexible but also rather rigid depending on the filler content.
Wood Plastic Composite floors, generally referred to as WPC floors, are similar to LVT floors. The core comprises thermosetting material mixed with wood fibre fillers and is generally stronger and much more rigid than the mineral based LVT core.
Thermoplastic material such as PVC, PP or PE may be combined with a mix of wood fibres and mineral particles and this may provide a wide variety of floor panels with different densities and flexibilities.
Moisture resistant HDF with a high resin content, and WPC floors, comprise stronger and more flexible core materials than conventional HDF based laminate floors and they are generally produced with a lower thickness.
The above mentioned floor types comprise different core materials with different flexibility, density and strengths. Locking systems formed in one piece with the core must be adapted to such different material properties in order to provide a strong and cost efficient locking function.
Definition of Some Terms
In the following text, the visible surface of the installed floor panel is called “front side” or “floor surface”, while the opposite side of the floor panel, facing the sub floor, is called “rear side”. The edge between the front and rear side is called “joint edge”. By “horizontal plane” is meant a plane, which extends parallel to the front side. Immediately juxtaposed upper parts of two adjacent joint edges of two joined floor panels together define a “vertical plane” perpendicular to the horizontal plane. By “vertical locking” is meant locking parallel to the vertical plane. By “horizontal locking” is meant locking parallel to the horizontal plane.
By “up” is meant towards the front side, by “down” towards the rear side, by “inwardly” mainly horizontally towards an inner and center part of the panel and by “outwardly” mainly horizontally away from the center part of the panel.
By “essentially vertical” surface or wall is meant a surface or a wall that is inclined less than 45 degrees against a vertical plane.
By “essentially horizontal” surface is meant a surface that is inclined less than 45 degrees against a horizontal plane.
By locking angle of a surface locking panels in the horizontal direction is meant the angle of the surface relative a vertical plane
By locking angle of a surface locking panels in the vertical direction is meant the angle of the surface relative a horizontal plane.
A tangent line defines the inclination of a curved wall or surface.
Related Art and Problems Thereof
For mechanical joining of long edges as well as short edges in the vertical direction and horizontal direction perpendicular to the edges several methods may be used. One of the most used methods is the angle-snap method. The long edges are installed by angling. Horizontal snapping locks the short edges. The vertical connection is generally a tongue and a groove and the horizontal connection is a strip with a locking element in one edge that cooperates with a locking groove in the adjacent edge. Locking by snapping is obtained with a flexible strip that during the initial stage of locking bends downwards and during the final stage of locking snaps upwards such that the locking element is inserted into the locking groove.
Similar locking systems may also be produced with a rigid strip and they are connected with an angling-angling method where both short and long edges are angled into a locked position.
Advanced so-called “fold down locking systems” with a separate and flexible tongue on a short edge, generally called “5G systems”, have been introduced where both the long and short edges are locked with an angling action. A floor panel of this type is presented in WO 2006/043893. It discloses a floor panel with a short edge locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a flexible bow shaped so called “banana tongue” cooperating with a tongue groove, for locking in a vertical direction. The flexible bow shaped tongue is inserted during production into a displacement groove formed at the edge. The tongue bends horizontally along the edge during connection and makes it possible to install the panels by vertical movement. Long edges are connected with angling and a vertical scissor movement caused by the same angling action connects short edges. The snapping resistance is low and only a low thumb pressure is needed to press the short edges together during the final stage of the angling. Such a locking is generally referred to as “vertical folding”.
Similar floor panels are further described in WO 2007/015669. This invention provides a fold down locking system with an improved flexible tongue so called “bristle tongue” comprising a straight outer tongue edge over substantially the whole length of the tongue. An inner part of the tongue comprises bendable protrusions extending horizontally along the tongue body.
The above known fold down “5G system” has been very successful and has captured a major market share of the premium world laminate and wood flooring markets. The locking is strong and reliable mainly due to the flexibility and pretension of the separate flexible tongue that allows a locking with large overlapping essentially horizontal locking surfaces.
The 5G system and similar system have been less successful in the low priced market segments. The major reason is that the cost of the separate tongues and investments in special inserting equipment that is needed to insert a flexible tongue into a displacement groove are regarded as rather high in relation to the rather low price of the floor panels.
Several attempts have been made to provide a fold down locking system based on a vertical snapping function that may be produced in one piece with the core in the same way as the one piece horizontal snap systems. All such attempts have failed especially when a floor panel comprises an HDF core. This is not a coincidence. The failure is based on major problems related to material properties and production methods. Several of the known locking systems are based on theoretical geometries and designs that have not been tested in industrial applications. One of the main reasons behind the failure is that bending of vertically protruding parts that are used for the vertical locking of edges is limited to about 50% of the floor thickness or to about 4 mm in an 8 mm thick laminate floor panel. As comparison it may be mentioned that a protruding strip for horizontal snapping may extend over a substantial distance from the upper edge and may protrude 8-10 mm beyond the upper edge. This may be used to facilitate a downward bending of the strip and the locking element. Other disadvantages compared to horizontal snapping are that HDF comprises a fibre orientation substantially parallel with the floor surface. The material properties are such that bending of horizontally protruding parts is easier to accomplish than bending of vertically protruding parts. Furthermore, lower parts of an HDF board comprise a higher density and a higher resin content than middle parts and such properties are also favorable for the horizontal snapping systems where the strip is formed in the lower part of the core.
Another circumstance that has supported market introduction of the horizontal snap systems is the fact that a hammer and a knocking block may be used to snap the short edges. Fold down systems are so called tool-less systems and the vertical locking must be accomplished with hand pressure only.
It would be a major advantage if a one-piece fold down locking system may be formed with a quality and locking function similar to the advanced 5G systems.